A New ILI Tool for Metal Loss Inspection of Gas Pipelines Using a Combination of Ultrasound, Eddy Current and MFL

The two prevailing technologies in in-line inspection (ILI) of pipelines used for metal loss detection are magnetic flux leakage (MFL) and ultrasonic testing (UT). The ultrasonic method provides a more precise depth sizing as a direct measurement of the remaining thickness of the pipe wall is obtained. The advantage of providing more precise defect data leads, in turn, to a more accurate and reliable defect assessment thus reducing follow-up costs for the pipeline operator. As conventional ultrasonic tools, which are based on piezoelectric transducers, require a liquid coupling medium to couple the ultrasonic energy into the pipe wall, this technology is readily applicable to the majority of liquids pipelines, but not to gas pipelines (unless a batch of liquid is used). In order to apply ultrasonic ILI technology for metal loss inspection to gas pipelines directly, a new tool was developed based on the EMAT (electro-magnetic acoustic transducer) principle by which ultrasound is generated in the surface of the pipe wall through electromagnetic interaction. EMAT sensors utilize coils for sending and receiving ultrasound. Since coils can also be used to pick up MFL signals and eddy current signals, the sensors were designed such that, apart from the ultrasonic signals, these additional signals are recorded simultaneously. The availability of three simultaneous, independent measurements allows for considerable improvement with regard to both defect sizing and feature discrimination. In the paper, the new sensor concept and the setup of the ILI tool are described. First results are presented and discussed.